This application claims the priority of German patent document 102 43 495.6, filed Sep. 19, 2002 (PCT International Application PCT/EP2003/009645, filed Aug. 30, 2003), the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method for operating a drive train of a motor vehicle.
European patent document EP 0 676 566 A1 discloses a method for operating a drive train of a motor vehicle with an automatic transmission that can be connected to a drive motor (in the form of an internal combustion engine), via a clutch. The transmission is shifted up when the clutch is closed, and the necessary deceleration of an input shaft of the transmission during a synchronization phase is carried out by the internal combustion engine. In this context, a profile parameter in the form of a gradient, of a rotational speed of the internal combustion engine is determined by a control device during the synchronization phase. A current gradient is established by means of the determined gradient and a pre-stored gradient and is used to predetermine a profile of the rotational speed of the internal combustion engine during a subsequent shifting up operation.
In view of the above, one object of the invention is to permit particularly accurate predetermination of the profile of the rotational speed of the drive motor when there is an actuated changed in the rotational speed.
This and other objects and advantages are achieved by the method according to the invention, for operating a vehicle drive train that includes a drive motor (for example, in the form of an internal combustion engine) and an automatic variable speed transmission. A driving off element in the form of a clutch or a hydrodynamic torque converter can be arranged between the drive motor and the automatic variable speed transmission. The clutch may be, for example, as a friction clutch, and may be actuated by an actuator element or a driver of a vehicle. (In an automatic variable speed transmission, switching elements can be actuated by means of actuator elements.) The variable speed transmission may be synchronized or nonsynchronized, and can also have a front-mounted transmission, for example by means of a split group.
The drive motor has actuator elements which are actuated by a control device. For example, the control device can predefine an injection quantity of a fuel, an ignition time or the use of what are referred to as engine brakes, for example in the form of an exhaust flap or a constant throttle.
The control device processes a rotational speed of the drive motor which it senses by means of a rotational speed sensor, which is fed to it by a further control device or is obtained from the rotational speed of the drive motor. For example, it is possible to process the rotational speed of a transmission input shaft which can be coupled to the drive motor by means of the clutch. When there is a request for a change in rotational speed of the drive motor from a starting rotational speed to a target rotational speed, the control device actuates the actuator elements in such a way that the target rotational speed is set. The target rotational speed can remain the same during the change or can change. For example, during a shifting operation from an original gear speed into a target gear speed of the variable speed transmission with the clutch closed, the rotational speed of the drive motor must be set to a synchronization speed of the target gear speed during a synchronization phase. The synchronization speed of the target gear speed is proportional here to a speed of the motor vehicle. If the speed of the motor vehicle changes during the synchronization phase, the synchronization speed of the target gear speed, and thus the target rotational speed of the change in rotational speed, also change.
When there is an actuated change in rotational speed of the drive motor during a neutral position of the variable speed transmission (that is, when no gear speed is engaged or while the clutch is opened), current profile parameters, for example in the form of a gradient, of the change in rotational speed are established. As a result, during the establishment of the parameters there is no connection between the input shaft and an output shaft of the variable speed transmission.
Corrected profile parameters are then established using previously stored profile parameters and the current profile parameters. The previously stored profile parameters are stored here in the control device of the drive motor or in some other control device. These values can be stored permanently or may be variable. The profile of the rotational speed of the drive motor is predetermined by means of the corrected profile parameters in selected operating states, for example when there is a shifting operation of the variable speed transmission.
The determination of the current and corrected profile parameters can be carried out by the control device of the drive motor or by a further control device (for example a control for the variable speed transmission). It is also possible for the current profile parameters to be determined by a control device, for example the drive motor, and for the corrected profile parameters to be determined by some other control device, for example the variable speed transmission.
Profile parameters of the change in rotational speed may be, for example, a gradient of the change in rotational speed between the starting rotational speed and the target rotational speed, a plurality of gradients for successive sections of the change in rotational speed or parameters of a spline approximation which is known per se.
A gradient of the change in rotational speed is established, for example, by measuring the rotational speed at various times and establishing the gradient using the differences in rotational speed which result from the measured rotational speeds, and the time intervals between the measurements. Furthermore, other methods for establishing gradients which are known to a person skilled in the art are applied.
A plurality of intermediate values of gradients can be calculated for successive sections during the change in rotational speed. The current gradient can be determined by averaging of the intermediate values of the gradients. During the averaging process all the intermediate values of the gradients can be weighted identically or else differently. Alternatively, the gradient may be determined only once, for example between two rotational speed values which lie near to the starting rotational speed or the target rotational speed. As a result, fluctuations in rotational speed which are superimposed on the actuated change are not taken into account.
When a change in rotational speed is calculated in advance, the profile can be composed of a plurality of straight segments with different gradients.
The parameters of a spline approximation of the rotational speed profile may be determined in a manner known per se, from measured rotational speed values and the associated time periods.
The corrected profile parameters are determined as a function of a starting rotational speed and/or target rotational speed of the change in rotational speed. The determination can also depend here only on the difference between the starting rotational speed and target rotational speed.
The invention makes use of the proposition that the gradient of the rotational speed during an actuated change in rotational speed is not constant. Rather, it is dependent, inter alia, on the rotational speed of the drive motor. For example, when no fuel is injected, what is referred to as an engine drag torque (that is, a negative torque) is produced, which reduces the rotational speed of the drive motor. The engine drag torque drops as the rotational speed of the drive motor decreases, so that the absolute value of the gradient becomes smaller as the rotational speed of the drive motor decreases when there is an actuated reduction in the rotational speed. Furthermore, the effect of engine brakes for reducing the rotational speed is also dependent on the rotational speed of the drive motor. (Thus, the braking effect of an exhaust valve at high rotational speeds is significantly greater than at low rotational speeds.) In addition, reaction times which greatly influence the required time period between the starting rotational speed and the target rotational speed (and thus the resulting gradient) come about between the actuation of the actuator elements of the drive motor and an effect on the rotational speed. For example, the time period between the actuation of an increase in torque and the start of a change in the rotational speed may be more than 100 ms. When a reduction in the rotational speed is supported by closing an exhaust flap, an exhaust gas counterpressure must first build up in order for an increased gradient to be subsequently brought about. When there is a small difference between the starting rotational speed and target rotational speed, this reaction time has a greater effect on the profile parameters (for example on the gradient which results between the starting rotational speed and target rotational speed) than when there is a large difference in rotational speed. As a result, the current profile parameters are also dependent on the difference in rotational speed.
When the current and the corrected profile parameters are determined as a function of the starting rotational speed and/or the target rotational speed, different profile parameters can be determined for different starting rotational speeds and/or target rotational speeds as well as various differences in rotational speed. When a profile of the rotational speed of the drive motor is predetermined it is then possible in each case to use a profile parameter which corresponds to the current starting rotational speed and/or target rotational speed. As a result, the profile of the rotational speed of the drive motor can be predetermined particularly accurately when changes in rotational speed are actuated.
Thus, when there is a change from an original gear speed into a target gear speed of the variable speed transmission, the actuator elements of the variable speed transmission are actuated in such a way that, when a desired distance from the synchronization speed is reached, the target gear speed is engaged, taking into account the delay times of the actuator elements. This permits particularly comfortable and rapid changes of gear speed.
In addition, the pre-stored profile parameters can be stored as a function of the starting rotational speed and the target rotational speed.
According to a further embodiment of the method according to the invention, when there is an actuated change in rotational speed, not only a corrected gradient but also a current reaction time are determined, and a corrected reaction time is established using the current reaction time and a pre-stored reaction time. The current reaction time is determined as a time period between an actuation time of an actuator element and a significant change in a state variable of the drive train (for example, the rotational speed, the gradient of the rotational speed or the torque which is output by the drive motor). The current reaction time can be established both when the actuator element is connected into the circuit and when it is disconnected from it. A significant change in the state variable is achieved if the change exceeds an adjustable limiting value. The limiting value may be dependent here on state variables of the drive train, for example the rotational speed or the temperature of the drive motor. For the calculation and pre-storage of the reaction time the same described possibilities and alternatives apply as to the calculation and the pre-storage of the gradient.
The determination of the gradient is not started until after the current reaction time has expired. As a result, a starting rotational speed can be obtained which differs slightly from that which is obtained when the determination is carried out without considering the reaction time. The gradient established in this way is independent of the reaction time of the actuator elements, and thus also of the difference in rotational speed between the starting rotational speed and target rotational speed. Calculation of the rotational speed of the drive motor in advance in selected operating states is therefore very accurate.
In one embodiment of the invention, the corrected gradient and/or the corrected reaction time are determined as a function of the starting rotational speed and/or target rotational speed. As a result, the described different effects of the actuator elements are taken into account with different rotational speeds of the drive motor. The calculation of the rotational speed in advance is therefore particularly accurate.
In one embodiment of the invention, the corrected gradient and/or the corrected reaction time are determined by averaging the pre-stored values and the current values, ensuring a continuous approximation to the actual conditions. In addition, this prevents excessive changes in the corrected values, which could adversely affect control parameters of the drive train. In addition, an incorrect determination of a current value cannot have excessive effects on the corrected values.
For example, averaging using a weighted sum can be carried out. In such a case the current and pre-stored values are multiplied by the same or different factors and then added. The corrected values are then established by dividing the sum by the sum of the aforesaid factors.
One or more pre-stored values can be included in the averaging.
In another embodiment of the invention, deviations of the current gradient and/or the current reaction time from the pre-stored values are determined. If the deviations exceed adjustable limiting values, the pre-stored values are adopted for the corrected gradient and/or for the corrected reaction time. The limiting values may be dependent on the number of adaptation steps, the starting rotational speed and/or target rotational speed, on state variables of the drive train and/or on actuating variables of the drive motor. Incorrectly determined values can thus be excluded from consideration.
In one embodiment of the invention, the corrected gradient and/or the corrected reaction time are stored and used as pre-stored values in the subsequent determination of the corrected gradient and/or of the corrected reaction time. The storage can also be retained when the motor vehicle is started up again after having been parked. As a result there is continuous adaptation of the corrected values to the actual conditions and changes over the service life of the motor vehicle can be taken into account.
It is possible in each case to store only the corrected value or, in addition to a basic value, to store a deviation from the basic value. The deviation may be stored, for example, as a correction factor or a correction value which is added to the basic value. As a result, the changes can be reversed and the adaptation restarted. A restart may take place, for example, when an actuator element is exchanged. Furthermore, relatively small changes can be resolved and thus stored since the deviations do not differ so much, and thus a higher resolution of the count value is possible with the same storage space. In addition, a reduction in the quantity of data to be stored by the control device of the variable speed transmission can be achieved by storing the basic values in a different control device, for example the control device of the drive motor.
In still another embodiment of the invention, it is established how often the corrected gradient and/or the corrected reaction time have been determined. The averaging is dependent on the established frequencies. As a result, greater account can be taken of the current values (for example at the start of the adaptation of the values, when the corrected values have not yet been established often), so that more rapid adaptation of the values can be achieved. After an adjustable number of adaptation steps it is possible to assume that the adaptation is good. As a result, the influence of the current values can be reduced. For example, given a weighted sum the factors can change with the number of adaptation steps.
The weightings can also be dependent here on the starting rotational speed and/or target rotational speed, on state variables of the drive train and/or on manipulated variables of the drive motor.
In still another embodiment of the invention, the corrected gradient and/or the corrected reaction time are established as a function of state variables of the drive train. (State variables of the drive train are, for example, the temperature of the drive motor, the temperature of the variable speed transmission or the setting of a front-mounted transmission of the variable speed transmission.) The storage of the values and the predetermination of the rotational speed of the drive motor are then also carried out while taking into account state variables of the drive train. This permits particularly accurate predetermination to be carried out.
In one embodiment of the invention, the corrected gradient and/or the corrected reaction time are established as a function of actuated manipulated variables of the drive motor. (Manipulated variables are, for example, the fuel injection quantity, the ignition time or actuated engine brakes.) The storage of the values and the predetermination of the rotational speed of the drive motor are then also carried out taking into account the manipulated variables. This permits particularly accurate predetermination to be carried out.
In another embodiment of the invention, when there is a gear speed change of the variable speed transmission, a gear speed is selected as a function of the corrected gradient and/or the corrected reaction time. When carrying out a shifting operation it is necessary to ensure that, after the target gear speed has been engaged, the drive motor is at an appropriate operating point (for example, that the rotational speed is not too high and not too low). During the shifting of a variable speed transmission the force flux from the drive motor to drive vehicle wheels is interrupted, and it is not possible to apply any drive torque. The speed of the motor vehicle may thus change greatly during the shifting process depending on the driving resistances, for example load or uphill/downhill travel. The duration of a shifting process can be calculated very accurately in advance using the corrected gradient and/or the corrected reaction time. As a result, given known or calculated driving resistances, the speed of the motor vehicle can be determined very accurately when the target gear speed is engaged. The operating point of the drive motor in the target gear speed can therefore be determined in advance and checked. If the operating point which is calculated is unfavorable, the selection of the target gear speed can be corrected, and a particularly advantageous target gear speed can be selected. In addition, shifting processes which cannot be carried through to their conclusion are suppressed.
According to a further feature of the invention, when the drive train is initially put into operation (in particular, when the variable speed transmission is in the neutral position), the drive motor is actuated in such a way that changes in rotational speed occur. Initial operation occurs, for example, when the drive train has been installed for the first time or after an assembly (for example the drive motor) is replaced. During the actuated changes in rotational speed, reaction times are determined as a time period between an actuation time and the time at which a change in a state variable of the drive motor exceeds an adjustable limiting value, and/or gradients of the changes in rotational speeds are determined. The reaction times and/or gradients which are determined are determined and stored in the control device of the drive motor or some other control device, for example of the variable speed transmission. As a result, the profile of the rotational speed of the drive motor can be calculated in advance in selected operating states, for example during the shifting processes of the variable speed transmission.
The sequence of actuation can be stored in a control device of the drive train and started by means of a signal, for example a momentary contact switch or a connected signal transmitter. Alternatively, the sequence can also be stored on an additional device which can be connected in a signal transmitting fashion to one or more control devices of the drive train. The additional device can transmit the actuation signals to the control device of the drive motor on request. A further possibility is for the driver of the vehicle to start a learning process by means of a signal, and to influence the torque (and thus the rotational speed of the drive motor) by means of an accelerator pedal.
The method according to the invention permits calculation in advance, immediately after initial operation, even if no advance information whatsoever is available about the operating behavior of the drive motor. As a result, for example when there is a change in gear speed of the variable speed transmission, an advantageous selection of the target gear speed, as described above, is possible immediately.
In one embodiment of the invention, the gradient and/or the reaction time are established as a function of:                the starting rotational speed and/or target rotational speed of the change in rotational speed;        state variables of the drive train; and/or        actuated manipulated variables of the drive motor.        
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.